The present invention relates to a method for the emergency braking of a wind power plant, in which at least one rotor blade of the wind power plant is adjusted in its feathering position. Furthermore, the invention relates to a wind power plant with at least one rotor blade and at least one rotor blade pitch device, which can set the blade pitch angle for the at least one rotor blade and can move the at least one rotor blade into its feathering position upon receipt of a control signal for an emergency braking.
The blade pitch angle of the rotor blade is defined as the angle that encloses the chord of the rotor blade with the rotation plane.
The feathering position of the rotor blade, also sometimes called the sail position, is the position of the rotor blade, in which the chord of the rotor blade is approximately perpendicular to the rotation plane of the rotor blade. In the feathering position, either the front edge or the rear edge of the rotor blade is turned into the wind such that no more lift can be created on the blade profile.
It is generally known to also move the rotor blades of the wind power plant into a feathering position during an emergency run with a nearly constant speed.
An apparatus for the pitch control of the sail position of the blade or blades of a wind turbine is known from DE 33 20 685 C2, the entire contents of which is incorporated herein by reference. It is described that the pitch control of the sail position with a constant, high speed can lead to excess blade load due to the considerable slowing (negative) torque and the reverse thrust that can be created by the blades. It is thus suggested, when moving the rotor blades into the sail position after the blade angle has been increased by up to one point in that the air flow over the blades no longer creates a positive torque on the wind turbine rotor, to reduce the speed of the pitch control of the sail position in order to minimize the slowing torque and the reverse thrust created by the blades and thus to minimize the blade load. It is also noted that, for safety reasons, the reduction of the pitch control speed when the blades near their sail position should not take place at the cost of the pitch control of the sail position with maximum speed while the air flow over the blades generates a positive shaft torque.
A wind energy plant with individual pitch devices is known from DE 10 2005 034 899 A1, the entire contents of which is incorporated herein by reference. When moving the rotor blade into its feathering position, a selector is provided that selects a controller regime at the beginning of the moving procedure that provides a high pitch control speed for the rotor blade. At point in time t2, as of which the rotor blade has reached a critical blade angle of attack θ0, a lower pitch control speed is selected for the rotor blade.
A method and an apparatus for the braking of a wind power plant are known from EP 1 788 237 A2, the entire contents of which is incorporated herein by reference. It is provided here that, if the rotor blades are moved from a first position to a second position, the blade pitch angle changes with a first speed and then is pitch controlled with a second speed, wherein the second speed is slower than the first speed.
A method for the pitch control of the rotor blades during the stopping of the rotor is known from WO 2009/010059 A2, the entire contents of which is incorporated herein by reference. In this method, the rotor blades are moved into a position, in which no thrust can be absorbed by the rotor. When there is aerodynamic thrust, the rotor is then controlled such that the thrust is mainly zero or works against the movement direction of the tower with its first natural frequency.
A method for the stopping of the rotor of a wind power plant is known from EP 1 701 034 A2, the entire contents of which is incorporated herein by reference, in which the rotor blade is moved during a first vibration phase I with a first pitch control speed. In a directly subsequent phase II, in which the mast of the wind power plant is tilted against the wind, the pitch control speed of the rotor blade is reduced until the mast of the wind power plant has reached its maximum amplitude against the wind. In the phase III following the swinging back of the mast, the rotor blade is moved again with the first pitch control speed. The pitch control process thereby takes place within the first seconds.
The object of the invention is to reduce the loads on the rotor blades and the rotor blade connections and the tower head vibrations during the emergency braking of the wind power plant.